1. Field of the Invention
This invention relates to a method and apparatus for obtaining samples of blood for diagnostic purposes.
2. Discussion of the Art
The prevalence of diabetes has been increasing markedly in the world. At this time, diagnosed diabetics represented about 3% of the population of the United States. It is believed that the total actual number of diabetics in the United States is over 16,000,000. Diabetes can lead to numerous complications, such as, for example, retinopathy, nephropathy, and neuropathy.
The most important factor for reducing diabetes-associated complications is the maintenance of an appropriate level of glucose in the blood stream. The maintenance of the appropriate level of glucose in the blood stream may prevent and even reverse many of the effects of diabetes.
Glucose monitoring devices of the prior art have operated on the principle of taking blood from an individual by a variety of methods, such as by needle or lancet. An individual then coats a paper strip carrying chemistry with the blood, and finally insert the blood-coated strip into a blood glucose meter for measurement of glucose concentration by determination of change in reflectance.
The medical apparatus of the prior art for monitoring the level of glucose in the blood stream required that an individual have separately available a needle or lancet for extracting blood from the individual, strips carrying blood chemistry for creating a chemical reaction with respect to the glucose in the blood stream and changing color, and a blood glucose meter for reading the change in color indicating the level of glucose in the blood stream. The level of blood glucose, when measured by a glucose meter, is read from a strip carrying the blood chemistry through the well-known process of reading reflectometers 15 for glucose oxidation.
Generally lancets comprise a blade and a pressable end opposed thereto, with the blade having an acute end capable of being thrust into skin of a human. By striking the pressable portion, the acute end of the blade will pierce the skin, for example, of the finger. The finger lancet is primarily used to obtain small volumes of blood, i.e., less than 1 mL. Diabetics use the finger lancet to obtain volumes of blood less than 25 .mu.L for analysis for glucose. A small amount of blood for the blood test will ooze out of the skin. There are many small blood vessels in each finger so that a finger can be squeezed to cause a larger drop of blood to ooze. The finger is one of the most sensitive parts of the body; accordingly, the finger lancet leads to even more pain than what would be experienced by extracting blood via lancet at a different body site. The finger lancet presents another problem because of the limited area available on the fingers for lancing. Because it is recommended that diabetics monitor their blood glucose levels four to six times per day, the limited area on the fingers calls for repeated lancing of areas that are already sore. Because fingers are sensitive to pain, it is a recent tendency that the arm is subjected to blood sampling. See, for example, U.S. Pat. No. 4,653,513. The device of U.S. Pat. No. 4,653,513 comprises a cylindrical housing and a lancet support, which has a gasket or flexible portion slidably accommodated in the housing. Springs will retract the lancet support to thereby reduce air pressure in the housing so that it sucks a blood sample, automatically and immediately after a lancet pierces the skin. See also U.S. Pat. No. 5,320,607, which discloses a device comprising a sealed vacuum chamber in a state of preexisting reduced pressure, a support member for the sealed vacuum chamber, the support member defining a suction portion adjacent the sealed vacuum chamber, the suction portion, in cooperation with the sealed vacuum chamber, exposing an area of the skin of a patient to a reduced pressure state when the device is actuated, and means arranged within the suction portion for slightly rupturing a portion of the area of skin of the patient exposed to the reduced pressure state.
Because the blood volume requirements for a standard glucose test strip is typically 3 .mu.L or more, an area of the body that can generate that much blood from a lancet wound must be used. It is believed, however, that improvements in glucose test strip technology will reduce the volume of blood needed to 1 to 3 .mu.L. Because the finger is well supplied with blood and the amount of blood can be increased by squeezing the finger after lancing, the finger is the currently preferred body site for lancing, even though lancing of the finger is painful.
A less painful technique for obtaining body fluids could be found if a reliable method were found for lancing a body part that is less sensitive to pain than the finger and obtaining a useful amount of blood from that body part. A body part such as the forearm is much less sensitive to pain than the finger, but the amount of blood resulting from the lancing procedure is generally of an inadequate volume for use with current detection technology. Ways of increasing blood flow to the finger are common knowledge. The recommendation is made to diabetics to run their finger under hot water prior to lancing to improve the blood flow in the finger and the amount of blood collected from the finger. Running hot water over a body part to improve blood flow is impractical for areas such as the forearm or thigh. The availability of hot water is also a concern.
It would be desirable to develop a technique and apparatus for obtaining blood for diagnostic purposes in a painless, reliable manner.
Conventional lancing devices, such as those described in U.S. Pat. Nos. Re. 32,922, 4,203,446, 4,990,154, and 5,487,748, accept commercially available, disposable lancets. Most conventional lancing devices are not integrated with a diagnostic instrument. A conventional lancing mechanism typically consists of a housing, a guided shaft having a lancet holder at one end, a main spring (usually helical) that supplies the mechanical energy to axially accelerate the shaft, and a return spring that partially retracts the shaft after lancing has occurred. The user must first insert a lancet into the holder, then manually slide the shaft until the main spring is compressed and the shaft is locked into its "cocked" position, then place the device against the skin, then press a trigger, which releases the shaft, thereby driving the lancet into the skin. The lancet is quickly retracted from the skin by the force of the return spring.
Conventional lancing devices would have several disadvantages for an apparatus that combines the processes of lancing, fluid collecting, and analyte sensing into one automated instrument. The first disadvantage is the necessity of manually cocking the lancing mechanism prior to each use. Manual cocking is inconvenient for the user and generally adversely affects the automated characteristics of an integrated instrument. Manual cocking also prohibits rapid, sequential lancing of the target skin. Sequential lancing could increase the volume of biological fluid collected. The second disadvantage is that the mechanical trigger can be accidentally pressed by the user if the device is mishandled. Accidental triggering of the lancet could injure the user and cause technical problems within an automated lancing system. The user would be further inconvenienced by having to re-cock the mechanism after accidental triggering. The third disadvantage is that the conventional return spring is generally not able to completely retract the lancet, due to the opposing force of the main spring. Partial retraction may subject the user to accidental punctures when handling the instrument before or after use, particularly when the lancet is located near other disposable components, such as fluid sample collection strips.
It would therefore be desirable to provide a lancing device that eliminates one or more of the foregoing disadvantages.